Angus Deaton, an economist, and Daniel Kahneman, a Nobel prize-winning psychologist, both from Princeton University, analyzed responses to the Gallup-Healthways Well-Being Index -- 450,000 survey responses from 2008 and 2009.
"The survey asks clear questions about life evaluation as well as emotional well being," Deaton told the Gallup Management Journal.
People who evaluate their lives based on their achievements -- if they've accomplished the goals they've set, are financially secure and are emotionally fulfilled, were more likely to have a high life evaluation, the researchers found.
"Having goals that you can meet is essential to life satisfaction," Kahneman said. "Setting goals that you're not going to meet sets you up for failure."
People with good emotional well being seem to get it via social contact, the researchers said.
"Emotional happiness is primarily social," Kahneman said. "The very best thing that can happen to people is to spend time with other people they like. That is when they are happiest."
The finding indicated $75,000 is the limit needed to be happy even in large expensive cities, Kahneman said.
Deaton and Kahneman said they are not certain why, but the data are clear: Even in cities expensive to live in, incomes more than $75,000 aren't correlated to greater happiness.